In 1961 Margaret Sparrow's husband, a trainee doctor, threw a couple of sample boxes of pea-green pills on the kitchen table and said "chomp away at these". Being the adventurous type, Sparrow swallowed them down.

They were newfangled contraceptives which, if they worked, could help keep their young family to two. Whether she was aware of it then or not, Sparrow was one of the first women in New Zealand to take the Pill. At the time, she was oblivious to the power of the little tablets she was gulping; not of their side effects, their chance of success, nor the enormous social implications they were about to have on the world.

"I knew absolutely nil about them but I'm one of those people who likes trying new things. Fortunately I had no side effects and I kept remembering to take them," she says. "I was the perfect candidate - married, just had my second child, was fit and healthy. I never saw a doctor; never had my blood pressure checked. I lived off free samples for years."

In the years to follow, Dr Margaret Sparrow would become one of New Zealand's leaders in sexual health and a major proponent of the Pill. "I don't think I realised at the time how revolutionary it was ... it really was one of the most important changes for women in history. It's a wonder there's no statue erected to the Pill," says Sparrow, now retired in Wellington. This month the Pill celebrates its 50th year on the world's pharmacy shelves.

During that time - a fundamental era for women's health, professional and social status - oral contraception has become safer and easier to take, its side effects better understood, its stigma almost vanished. In April 1967, Time magazine's cover story, titled "Freedom From Fear", described how in six years the Pill had changed and liberated the "sex and family life" of a large chunk of the United States population, and promised to do the same for much of the world.

"The Pill, as oral contraceptives are now universally known, may well have as great an impact on the health of billions of people yet unborn as did the work of Pasteur in revealing the mechanism of infections, or of Lister in preventing them," the article stated. "For if the Pill can defuse the population explosion, it will go far toward eliminating hunger, want and ignorance."

Perhaps the Pill was not the magic little bullet the world had hoped for; today, of the 210 million women who fall pregnant each year, around 80 million pregnancies are still unplanned. According to the World Health Organisation, 20 million of those women have abortions and 68,000 die as a result. Yet the Pill has undoubtedly made a monumental impact on the lives of women globally - it sparked the sexual revolution and, for the first time, women could be in control of their fertility and their careers. Those little green pills went a long way to giving women equality.

While other forms of contraception have come on the world market since - the IUD, hormonal coils, implants and the not-so-successful female condom - the Pill is still the most common form of birth control in New Zealand, used by an estimated 202,000 women here. And for all the talk of the past two decades, the mythical Men's Pill may never be ingested. Instead, all research now points to "the Jab" as being the next big advance in birth control.

Last month the results of trials of a monthly contraceptive jab given to fertile Chinese men were released to the world, injecting new hope of an effective, and reversible, contraceptive finally being available to men. The concept of testosterone temporarily blocking sperm production is not new, but it has never been developed into a feasible contraceptive because of a lack of interest from pharmaceutical companies worldwide. That many women still don't trust men to be responsible for birth control may be playing a significant role in that.

Margaret Sparrow collects old condoms. Not used ones off the beach at Oriental Bay; but largely intact remnants from our contraceptive history. She is curator of a varied collection of alien and amoeba-like intrauterine devices, cervical caps, pill dials and prophylactics now on display at Family Planning's national office in Wellington.

"Whenever I removed a device from a woman that had been inserted overseas, I'd usually keep it for demonstrations, to show examples of methods used elsewhere. Then I started to collect old pills, condoms and spermicides," Sparrow says. A Wellington woman donated the contents of her parents' medicine cupboard: syringes, old abortion pills, and her father's prophylactic kit from World War II.

"A builder demolishing a house discovered a tiny cupboard in the floorboards of a bedroom and inside was this amazing silver box containing an old, perished condom. The gentleman was a very considerate lover - there was spermicidal cream in there too," Sparrow says. Before the Pill, the diaphragm and rubber condom were essentially the only form of contraception, with no advances on either since their invention in the mid-1800s. The history of the oral contraceptive doesn't fit neatly in a pill box. By the 1920s, scientists had figured out that hormones could inhibit ovulation but it wasn't until the 1950s that American birth control activist Margaret Sanger, with the financial help of International Harvester heiress Katharine McCormick (later dubbed the Mothers of the Pill), encouraged reproduction expert Gregory Pincus to try to create a "magic pill" to stop unwanted pregnancies.

Pincus determined that the hormone progesterone could restrain ovulation in rabbits, then found two US drug companies had created a synthetic progesterone. He used one created by chemists Frank Colton and Carl Djerassi in human trials in Puerto Rico. Four years later, on June 23, 1960, the first contraceptive pill - a combination of estrogen and progestin, called Enovid-10 - was approved by the Food and Drug Administration for use in the United States. This was one of the most significant medical advances in the 20th century, which for the first time did not treat an illness.

Those first pills that Sparrow took, introduced to New Zealand a year later, were Anovlar, Europe's first oral contraceptive. Here, the Pill was to be prescribed only to married women; there were fears it would encourage promiscuity among the unmarried. In 1970, Sparrow was working at Student Health Services at Victoria University when girls came in asking for contraceptive advice. "Ethically you weren't supposed to suggest the Pill if they weren't married, no matter what their age. I wasn't a member of the Medical Association then, so I didn't worry about that," Sparrow recalls.

"In my medical training, there had only been one lecture on contraception and it didn't include the Pill. I was really ignorant other than from my own experiences. So I knocked on the door of Family Planning and found doctors who were prescribing the Pill to unmarried women, who felt ethically it was right to protect women against unplanned pregnancy. I liked their approach, so I joined them. "There was a backlash - we were rocking the boat. You should be nice doctors - proper doctors obey the ethical guidelines. But I wasn't alone."

The early Pill was far from perfect - massive oestrogen levels in the combined pill brought side effects and health dangers. Scientists had yet to determine how low they could effectively reduce the hormones. Where the pills Sparrow swallowed had 100mcg of estrogen, today's pills contain around 20-30mcg. "Every now and then there'd be a scare story - blood clots or breast cancer. It was quite a concern, and there was truth to some of them when the estrogen levels were so high," Sparrow says.

"Everyone was concerned about the risks, especially when women died. But I never, ever felt I shouldn't be prescribing the Pill. I changed the way I prescribed it, I always tried the safest ones and I never suggested it to all women."

Even today's low-dose Pill is still not danger-free - there are risks of blood clots, heart attack or stroke for women who have other conditions like high cholesterol or diabetes, who are overweight or smoke. There's also a short-term increased risk of cervical cancer for those who take the Pill for five or more years, but cervical screening has improved.

Recent studies have found taking the Pill reduces ovarian cancer for up to 30 years after you stop taking it, and also protects against endometrial (lining of the womb) cancer. The progestin-only mini pill, introduced in 1973, cut out the risks associated with estrogen but had its own drawbacks - there was irregular bleeding and it was less effective.

Christine Roke, the national medical adviser for Family Planning in New Zealand, says the major changes to the chemistry of the Pill happened in the first decade, but it continues to be tweaked. "Each year there's the potential for new pills - a different progestin or a slightly different dose. But while they're tweaks for some, they may be a huge difference to other women - the difference between being able to take them or not."

1955 First trials of progesterone as a contraceptive on female volunteers in the United States and Puerto Rico.
1960 The US Food and Drug Administration approves the sale of Enovid-10 as a birth control pill.
1961 The oral contraceptive pill comes on to the New Zealand market - Anovlar. Also introduced in Britain, Europe and Australia.
1967 More than 12.5 million women worldwide are on the Pill.
1973 The mini pill, containing progestin only, is introduced.
1984 An estimated 50-80 million women around the world are on the Pill.
2009 Around 100 million worldwide take the Pill; an estimated 202,000 New Zealand women are on it.

Quick facts
The combined pill is 99 per cent effective if taken correctly; progestin-only pills are 96-99 per cent effective.
Ovarian cancer and endometrial cancer is reduced by 50 per cent for women on the combined pill, with a lower risk more than 30 years after stopping the Pill.
For every 10,000 pill users under the age of 30, an extra seven cases of breast cancer will be diagnosed; between 30 and 45 there will be an extra 40 cases.
The Pill can increase the risk of blood clots in the leg from 5 to 10-in-100,000 women each year to possibly more than eight times that rate with some pills.
In the early years, the Pill contained around 50-100mcg of oestrogen; most now contain around 20-30mcg. Progestin levels have been reduced to a 10th of their original level.